Just three days ago i had the same problem. i solved it like this:
WOFF is supported in FF 3.6+, Chrome 5.0+, Safari 5.1+, IE 9+ so your modern browsers are covered. as seen on caniuse.com
as far as older browsers (< IE 9) you just need the eot file. you get it by opening the google font css file in a browser in which you can change the useragent. If you change the useragent to ie 7 for example, the stylesheet will include the link to the eot file.
for example if you open this link with useragent ie 7 in chrome: Roboto Google Font css file
it will output this:
@font-face {
font-family: 'Roboto';
font-style: normal;
font-weight: 400;
src: url(http://themes.googleusercontent.com/static/fonts/roboto/v10/5YB-ifwqHP20Yn46l_BDhA.eot);
src: local('Roboto Regular'), local('Roboto-Regular'), url(http://themes.googleusercontent.com/static/fonts/roboto/v10/5YB-ifwqHP20Yn46l_BDhA.eot) format('embedded-opentype'), url(http://themes.googleusercontent.com/static/fonts/roboto/v10/2UX7WLTfW3W8TclTUvlFyQ.woff) format('woff');
}
so just grab the eot file url from the src:
http://themes.googleusercontent.com/static/fonts/roboto/v10/5YB-ifwqHP20Yn46l_BDhA.eot